From d550e89d21c822d9118057757c4b6e6d12fa295d Mon Sep 17 00:00:00 2001
From: Finn Teegen <fte@informatik.uni-kiel.de>
Date: Thu, 14 Jul 2022 12:05:59 +0200
Subject: [PATCH] Add MonadFix instance for Codensity

---
 src/Control/Monad/Codensity.hs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/Control/Monad/Codensity.hs b/src/Control/Monad/Codensity.hs
index 092e8f2..290ccc6 100644
--- a/src/Control/Monad/Codensity.hs
+++ b/src/Control/Monad/Codensity.hs
@@ -44,6 +44,7 @@ module Control.Monad.Codensity
 import Control.Applicative
 import Control.Monad (MonadPlus(..))
 import qualified Control.Monad.Fail as Fail
+import Control.Monad.Fix
 import Control.Monad.Free
 import Control.Monad.IO.Class
 import Control.Monad.Reader.Class
@@ -168,6 +169,9 @@ instance MonadPlus v => MonadPlus (Codensity v) where
   {-# INLINE mplus #-}
 #endif
 
+instance MonadFix v => MonadFix (Codensity v) where
+  mfix f = Codensity (\k -> mfix (lowerCodensity . f) >>= k)
+
 -- |
 -- This serves as the *left*-inverse (retraction) of 'lift'.
 --